/*
Copyright IBM Corp. 2016 All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

		 http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package stateleveldb

import (
	"bytes"
	"errors"

	"github.com/hyperledger/fabric/common/flogging"
	"github.com/hyperledger/fabric/common/ledger/util/leveldbhelper"
	"github.com/hyperledger/fabric/core/ledger/kvledger/txmgmt/statedb"
	"github.com/hyperledger/fabric/core/ledger/kvledger/txmgmt/version"
	"github.com/hyperledger/fabric/core/ledger/ledgerconfig"
	"github.com/syndtr/goleveldb/leveldb/iterator"
)

// 3个问题
// 1. 如何关联智能合约键值对与底层存储的键值对 数据隔离
// 2. 如何持久化区块的状态信息
// 3. 如何标识最新存储的区块编号

var logger = flogging.MustGetLogger("stateleveldb")

var compositeKeySep = []byte{0x00} // 组合键的分隔符
var lastKeyIndicator = byte(0x01)
var savePointKey = []byte{0x00}

// VersionedDBProvider implements interface VersionedDBProvider
type VersionedDBProvider struct {
	dbProvider *leveldbhelper.Provider
}

// NewVersionedDBProvider instantiates VersionedDBProvider
func NewVersionedDBProvider() *VersionedDBProvider {
	dbPath := ledgerconfig.GetStateLevelDBPath()
	logger.Debugf("constructing VersionedDBProvider dbPath=%s", dbPath)
	dbProvider := leveldbhelper.NewProvider(&leveldbhelper.Conf{DBPath: dbPath})
	return &VersionedDBProvider{dbProvider}
}

// GetDBHandle gets the handle to a named database
func (provider *VersionedDBProvider) GetDBHandle(dbName string) (statedb.VersionedDB, error) {
	return newVersionedDB(provider.dbProvider.GetDBHandle(dbName), dbName), nil
}

// Close closes the underlying db
func (provider *VersionedDBProvider) Close() {
	provider.dbProvider.Close()
}

// VersionedDB implements VersionedDB interface
type versionedDB struct {
	db     *leveldbhelper.DBHandle
	dbName string
}

// newVersionedDB constructs an instance of VersionedDB
func newVersionedDB(db *leveldbhelper.DBHandle, dbName string) *versionedDB {
	return &versionedDB{db, dbName}
}

// Open implements method in VersionedDB interface
func (vdb *versionedDB) Open() error {
	// do nothing because shared db is used
	return nil
}

// Close implements method in VersionedDB interface
func (vdb *versionedDB) Close() {
	// do nothing because shared db is used
}

// ValidateKey implements method in VersionedDB interface
func (vdb *versionedDB) ValidateKey(key string) error {
	return nil
}

// GetState implements method in VersionedDB interface
func (vdb *versionedDB) GetState(namespace string, key string) (*statedb.VersionedValue, error) {
	logger.Debugf("GetState(). ns=%s, key=%s", namespace, key)
	compositeKey := constructCompositeKey(namespace, key)
	dbVal, err := vdb.db.Get(compositeKey)
	if err != nil {
		return nil, err
	}
	if dbVal == nil {
		return nil, nil
	}
	val, ver := statedb.DecodeValue(dbVal)
	return &statedb.VersionedValue{Value: val, Version: ver}, nil
}

// GetStateMultipleKeys implements method in VersionedDB interface
func (vdb *versionedDB) GetStateMultipleKeys(namespace string, keys []string) ([]*statedb.VersionedValue, error) {
	vals := make([]*statedb.VersionedValue, len(keys))
	for i, key := range keys {
		val, err := vdb.GetState(namespace, key)
		if err != nil {
			return nil, err
		}
		vals[i] = val
	}
	return vals, nil
}

// GetStateRangeScanIterator implements method in VersionedDB interface
// startKey is inclusive
// endKey is exclusive
func (vdb *versionedDB) GetStateRangeScanIterator(namespace string, startKey string, endKey string) (statedb.ResultsIterator, error) {
	compositeStartKey := constructCompositeKey(namespace, startKey)
	compositeEndKey := constructCompositeKey(namespace, endKey)
	if endKey == "" {
		compositeEndKey[len(compositeEndKey)-1] = lastKeyIndicator
	}
	dbItr := vdb.db.GetIterator(compositeStartKey, compositeEndKey)
	return newKVScanner(namespace, dbItr), nil
}

// ExecuteQuery implements method in VersionedDB interface
func (vdb *versionedDB) ExecuteQuery(namespace, query string) (statedb.ResultsIterator, error) {
	return nil, errors.New("ExecuteQuery not supported for leveldb")
}

// ApplyUpdates implements method in VersionedDB interface
func (vdb *versionedDB) ApplyUpdates(batch *statedb.UpdateBatch, height *version.Height) error {
	dbBatch := leveldbhelper.NewUpdateBatch()
	namespaces := batch.GetUpdatedNamespaces()
	for _, ns := range namespaces {
		updates := batch.GetUpdates(ns)
		for k, vv := range updates {
			compositeKey := constructCompositeKey(ns, k)
			logger.Debugf("Channel [%s]: Applying key=[%#v]", vdb.dbName, compositeKey)

			if vv.Value == nil {
				dbBatch.Delete(compositeKey)
			} else {
				dbBatch.Put(compositeKey, statedb.EncodeValue(vv.Value, vv.Version))
			}
		}
	}
	// 标识最新区块
	dbBatch.Put(savePointKey, height.ToBytes())
	// Setting snyc to true as a precaution, false may be an ok optimization after further testing.
	if err := vdb.db.WriteBatch(dbBatch, true); err != nil {
		return err
	}
	return nil
}

// GetLatestSavePoint implements method in VersionedDB interface
func (vdb *versionedDB) GetLatestSavePoint() (*version.Height, error) {
	versionBytes, err := vdb.db.Get(savePointKey)
	if err != nil {
		return nil, err
	}
	if versionBytes == nil {
		return nil, nil
	}
	version, _ := version.NewHeightFromBytes(versionBytes)
	return version, nil
}

func constructCompositeKey(ns string, key string) []byte {
	return append(append([]byte(ns), compositeKeySep...), []byte(key)...)
}

func splitCompositeKey(compositeKey []byte) (string, string) {
	split := bytes.SplitN(compositeKey, compositeKeySep, 2)
	return string(split[0]), string(split[1])
}

type kvScanner struct {
	namespace string
	dbItr     iterator.Iterator
}

func newKVScanner(namespace string, dbItr iterator.Iterator) *kvScanner {
	return &kvScanner{namespace, dbItr}
}

func (scanner *kvScanner) Next() (statedb.QueryResult, error) {
	if !scanner.dbItr.Next() {
		return nil, nil
	}
	dbKey := scanner.dbItr.Key()
	dbVal := scanner.dbItr.Value()
	dbValCopy := make([]byte, len(dbVal))
	copy(dbValCopy, dbVal)
	_, key := splitCompositeKey(dbKey)
	value, version := statedb.DecodeValue(dbValCopy)
	return &statedb.VersionedKV{
		CompositeKey:   statedb.CompositeKey{Namespace: scanner.namespace, Key: key},
		VersionedValue: statedb.VersionedValue{Value: value, Version: version}}, nil
}

func (scanner *kvScanner) Close() {
	scanner.dbItr.Release()
}
